Various arrangements for lighting systems are known which provide both conventional and emergency lighting. Such emergency lighting is intended to be activated when the conventional lighting is no longer operative because the mains supply to the conventional lighting is no longer available or malfunctions. Emergency lighting is typically powered by a battery or other energy storage device. Conventional lighting is controlled by an on/off switch by means of which a user (or control system) can control whether the lighting is illuminated or not. Generally, emergency lighting is intended to be automatically illuminated when the absence of mains power or the malfunction of mains power for the conventional lighting is detected in some way. Emergency lighting may be used to allow escape from buildings that would otherwise be in darkness due to the inoperativeness of the conventional lighting.
Emergency lighting and conventional lighting may share components. For example, the same lamp (such as a gas discharge lamp or LED) and/or ballast may be used for both conventional and emergency lighting (“maintained mode”). Other components may also be shared.
A lighting system comprising emergency lighting and conventional lighting may be considered to have two operating modes. In a normal mode, when the direct mains supply is operating normally (within the normal voltage range), a switched mains input, controlled by an on/off switch, is monitored, and the lamp is illuminated or extinguished in dependence upon the switched mains input In an emergency mode, when the mains supply is not available or is malfunctioning (is outside the normal voltage range), the lamp is illuminated automatically, irrespective of the status of the switched mains input, using power from a battery or other storage element.
FIG. 1 shows the basic elements of such a known lighting system, designated generally at 1, which receives the switched mains input 3 and the direct AC mains input 5. The direct AC mains input 5 is filtered by input filter 7 (for harmonics, EMI, and power factor reasons) and rectified by rectifier 9 to which a SELV (Separated Extra Low Voltage) isolated DC-DC input converter 11 is connected
The lighting system further comprises a light source driver 13 (e.g. electronic ballast) and a light source 15 (e.g. LED lamp) powered by the input converter 11.
An electronic controller 17 controls the operation of the lighting system, including activating emergency lighting when appropriate.
FIG. 1 further shows a battery 19 which provides power in an emergency situation. Battery power is applied to the driver 13 and light source 15 when the controller 17 detects the failure of the mains supply 5.
The same light source driver 13 is used both in the emergency mode and the normal mode to supply current to the lamp 15 in this example, although this is not essential. The emergency mode is activated by the controller 17 when the direct mains input 5 is not available or malfunctions. The normal mode should be activated by the controller 17 when the direct mains 5 is present and operating correctly, and in this mode the lamp 15 is illuminated when the switched mains 3 is on. The voltage on the direct mains input 5 may be an AC voltage (e.g. 230V AC).
The controller 17 is powered by a controller supply 23, which itself is powered by the input converter 11. The controller supply 23 may be a Low Voltage Power Supply (LVPS). The controller 17 may be also powered from the battery 19.
When the direct mains input 5 is a normal AC mains signal the battery 19 is charged from the input converter 11 by battery charger 21 (via charger rail 46) under control of the controller 17.
In more detail, the input converter 11 receives the direct mains input voltage 5 and provides DC output to supply current to the light source driver 13 and battery charger 21. The switched mains input 3 is monitored either directly or indirectly by the controller 17. The controller 17 also determines whether or not the direct mains input 5 is operating normally.
When the controller 17 determines that the direct mains 5 is operating normally and that the switched mains input 3 is on, the electronic controller 17 activates the light source driver 13 to illuminate the lamp 15 and activates the battery charger to charge the battery 19.
When the controller 17 detects that the direct mains input 5 is not normal (emergency mode), the controller 17 activates the light source driver 13 using power from the battery 19 to illuminate the lamp 15 (irrespective of the status of the switched mains input 3).
When in the normal mode the electronic controller 17 may operate the light source driver 13 in a different manner to the emergency mode.
The controller 17 may determine the status of the switched live input 3 in any suitable manner. For example, it is known to apply the switched mains input 3 to a potential divider, and then to a voltage threshold detector with an isolation circuit, such as an opto-coupler. Typically, the mains input 3 is rectified by a rectifier before being applied to the voltage threshold detector and the isolation circuit. When the switched live input 3 is on, the output of the isolation circuit will be a pulsed signal, the presence of which can be detected by logic within the controller 17. When the switched live 3 input is off, the output of the isolation circuit will be a constant value (zero volts) and this can also be detected by logic of the controller 17. The controller 17 then operates the driver 13 and lamp 15 in accordance with the state of the switched mains input 3. The signal on the switched live input 3 which is interpreted as signal for the status of the emergency mode may have different shapes or states, depending on the definition of the system. A signal of zero volts as described above is just an example.
The lighting system 1 may comprise an interface 25, e.g. a DALI (Digital
Addressable Lighting Interface), that is connected to a DALI bus 26, for intensity control (dimming) and/or for maintenance and service control. DALI is a communication protocol widely used in lighting systems. A two wire serial communication arrangement establishes a master/slave communication between a central DALI controller (not shown) and the lighting system controller 17 by setting low and high levels of voltages. Data is transferred between the DALI controller and lighting system controller, by means of an asynchronous, half-duplex, serial protocol over a two-wire differential bus, with a fixed data transfer rate of 1200 bit/s. The DALI data is transmitted using Manchester encoding. The protocol standard sets high levels as voltage differences higher than a range of 9.5V up to 22.5V between the two wires.
Low levels are set as voltage differences of less than 6.5V down to −6.5V (either positive or negative). According to the protocol the current supply for the DALI communication has to be limited to 250 mA.
Depending on the type of mains voltage detected on the direct mains input 5, the controller 17 may put the driver 13 into different operation modes, e.g. to illuminate the lamp 15 at a given intensity level. The different types of operation depending on the type of detected mains voltage may be also programmed in the controller 17 and may be changed (e.g. by the DALI controller) through an interface (e.g. DALI interface). For example the dimming range can be limited due to the detected type of mains voltage or a certain dimming level can be selected (e.g. in emergency mode).
The lighting system may additionally include a test switch (to exercise auto-test routines) and a status indicator LED 29, connected to the controller 17.
It is desirable that the controller 17 is continuously powered. If the controller 17 does not receive power it will shut down and it will not be possible for the controller 17 to react to input signals in order to provide the desired illumination of the lamp 15. Such input signals may include the switched live input 3, instructions from the DALI interface 25 and operation of test switch 27. The controller 17, if deactivated, will also not be able to perform mains detection to determine whether the AC mains supply 5 is present and operating as normal, and so will not be able to detect an emergency situation and illuminate the lamp 15 in an emergency mode.
When the direct mains input 5 fails or malfunctions, the controller 17 is powered by the battery 19. Initially, the battery 19 may be able to provide sufficient power to operate the controller 17. In emergency situations, current being drawn from the battery 19 after a discharge event (emergency mode occurrence during which the lamp 15 has been illuminated by battery power) may be limited to very low levels whilst the direct mains input is not present (or is malfunctioning). The quiescent current from the battery 19 may be at a very low level (for example less than 100 μA). A battery of the nickel metal hydride (NiMh) type or a battery of a different type having a sensitive chemistry has a limited current output.
The lighting system 1 may have a “rest mode” which enables, for example, the emergency lighting to be switched off during a mains failure after a time when the premises have been fully evacuated. This prevents full discharge of the battery 19 by constant illumination of a lamp 15 when this is no longer necessary. This assists reoccupation of the premises because it stops full discharge of batteries. However, in the “rest mode” the amount of power available from a battery 19 can reach a very low level as the “rest mode” can last long periods where no recharge happens and the battery slowly discharges through parasitics and self-discharge.
The low level of current available from the battery makes it difficult to keep the controller 17 operating when the direct mains input 5 is not available (or malfunctioning). To mitigate this difficulty technologies have been developed to allow the integrated circuits used for implementing the controller 17 to operate in lower power states. However, in some cases such measures are not sufficient to allow the controller 17 to continue operating throughout an emergency situation where the direct mains input 5 is unavailable (or malfunctioning). This, disadvantageously, results in loss of control of the lighting system.
In general, it is an object of the present invention to provide a convenient auxiliary power supply for a lighting system. Such an auxiliary power supply may, for example, be used to power the controller 17 so that the controller can remain operative when the current available from the battery 19 is significantly diminished. However, it should be appreciated that the object of the invention is to provide an auxiliary power supply for general use in a lighting system, and not just for powering a controller like the controller 17 described above.